“It’s only been live for just more than a month, but Tumblr already has 50,000 users. So far, the site is free, and Tumblr says it will stay that way, though it might offer additional advanced features in the future for a fee.”

50,000 users is a good number. Hopefully, Tumblr will get more popular as it’s a very useful tool. I’m hoping they come out with a download version so that I can run it on my server.